What mistakes do students make with Forces and elasticity?

Subtracting the original length from the compressed length, giving a negative value. Put it right by using e = original length − compressed length. Treating compression as a different equation from extension. Put it right by recognising that the same relationship applies, with e representing compression. Forgetting to convert centimetres to metres before calculating compression. Put it right by converting all lengths to metres first.

What are the exam tips for Forces and elasticity in Combined Science AQA GCSE?

Label which length is original and which is compressed before subtracting, so the direction of the change is clear. State that e represents compression when the object is squashed, and keep the unit as metres. Use the same equation as for extension, but substitute the compression value for e.

AQA · GCSE · Combined Science

Course version: 8464 · Version from Sept 2018

This relationship also applies to the compression of an elastic object,…

Full specification wording

Forces and elasticity: This relationship also applies to the compression of an elastic object, where ‘e’ would be the compression of the object.

The force–extension relationship, force = spring constant × extension, also describes compression of an elastic object.

Checked against the AQA 8464 specification (opens in a new tab) on 20 September 2026.

Point 10 of 19

Study notes

From the checked teaching notes for this specification point.

The idea

What earns the marks

States that the force–extension relationship also applies when an elastic object is compressed.
Defines compression as the decrease in length of an elastic object under a compressive force.
Calculates compression using e = original length − compressed length.
Uses the same equation, force = spring constant × compression, with e representing compression.
Recognises that compression is measured in metres and that the spring constant is unchanged in meaning.
Applies the relationship only while the elastic limit is not exceeded.

Common mistakes and how to put them right

Subtracting the original length from the compressed length, giving a negative value.
Put it right by using e = original length − compressed length.
Treating compression as a different equation from extension.
Put it right by recognising that the same relationship applies, with e representing compression.
Forgetting to convert centimetres to metres before calculating compression.
Put it right by converting all lengths to metres first.

Exam tips

Label which length is original and which is compressed before subtracting, so the direction of the change is clear.
State that e represents compression when the object is squashed, and keep the unit as metres.
Use the same equation as for extension, but substitute the compression value for e.

Try the lesson

The start of the Forces and elasticity: This relationship also applies to the compression of an elastic object, where ‘e’ would be the compression of the object. lesson, made from checked teaching notes for this specification point.

Have a go first

A spring has an original length of 15 cm. A force is applied to squash the spring until its length is 11 cm. What is the compression, e, of the spring?

Tip: press 1 to 4 to choose

Listen

The force–extension relationship, force = spring constant × extension, also describes compression of an elastic object. In compression, the object shortens, and e represents the compression, the decrease in length. Compression is calculated as original length minus compressed length: e = L₀ − L. For example, a spring of original length 0.15 m compressed to 0.11 m has e = 0.15 m − 0.11 m = 0.04 m. The spring constant has the same meaning, and the force is the compressive force. Compression is still measured in metres, and the same equation applies as long as the elastic limit is not exceeded. A strong answer earns marks for these points. States that the force–extension relationship also applies when an elastic object is compressed. Defines compression as the decrease in length of an elastic object under a compressive force. Calculates compression using e = original length − compressed length. Uses the same equation, force = spring constant × compression, with e representing compression. A common slip: Subtracting the original length from the compressed length, giving a negative value. Instead, using e = original length − compressed length. Exam tip: Label which length is original and which is compressed before subtracting, so the direction of the change is clear.

See it

A top-down flowchart. Two boxes, 'Original length L₀' and 'Compressed length L', both lead into a box reading 'Compression e = L₀ − L'. That box leads to 'e represents compression, measured in metres', which leads to 'Force = spring constant × compression', which finally leads to 'Applies while the elastic limit is not exceeded'. — It shows how compression is calculated from original and compressed lengths and then used in the force–spring constant relationship.

Label the diagram

Some boxes have lost their names. Pick the right name for each number.

The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. Two boxes, 'Original length L₀' and 'Compressed length L', both lead into a box reading 'Compression e = L₀ − L'. That box leads to 'e represents compression, measured in metres', which leads to 'Force = spring constant × compression', which finally leads to 'Applies while the elastic limit is not exceeded'.

1Box 1
2Box 2
3Box 3

0 of 3 labelled

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